Merge pull request #78 from martinthomson/sdpwrap

Fixing c= ttl handling
Export tracks and accurately update state
Merge pull request #79 from ekr/MS_export_remote_tracks

Export tracks and accurately update state
added origin tests
Merge pull request #80 from nils-ohlmeier/multistream

added origin tests
SDP errors now report line numbers
Start testing serialization.
Merge pull request #81 from adamroach/sdp

SDP errors now report line numbers
Merge pull request #82 from docfaraday/multistream_unit_tests

Start testing serialization.
Adding a=group support